Feline Hyperthyroidism is one of the most common endocrine disorders in middle-aged and older cats. Reports estimate that one in three hundred cats are affected by hyperthyroidism. The thyroid glands are located in the neck and produce hormones that regulate cellular metabolism in all organs of the body.

The amount of thyroid hormone produced by the thyroid glands is regulated by the pituitary gland in the brain. The pituitary gland signals the thyroid glands to maintain proper levels of circulating thyroid hormone. This mechanism keeps cellular metabolism in balance. Most cases of feline hyperthyroidism are due to benign tumors called nodular hyperplastic goiters.

These tumors produce excess thyroid hormone and do not respond to regulation by the pituitary gland. Unfortunately, the thyroid tumor cannot always be palpated in the neck. Some cats will have thyroid tumor in the chest or other locations in the body. Any of these tumors can produce excessive amounts of thyroid hormone.

The signs and symptoms of hyperthyroidism are multi-systemic and relate to increased metabolic changes. Hyperactivity, weight loss, increased appetite, increased thirst, increased elimination, vomiting, diarrhea, panting, rapid heart rate, increased shedding, and occasionally lethargy have been observed. High blood pressure is a common clinical finding. Blindness due to retinal hemorrhage and heart disease (including heart failure) may also be associated with hyperthyroidism. Untreated hyperthyroidism is fatal.